Vascular diseases, such as atherosclerosis and the like, have become quite prevalent in the modem day. These diseases may manifest themselves in a number of ways, often requiring different forms or methods of treatment for curing the adverse effects of the diseases. Vascular diseases, for example, may take the form of deposits or growths in a patient's vasculature which may restrict, in the case of a partial occlusion, or, stop, in the case of a total occlusion, blood flow to a certain portion of the patient's body. This can be particularly serious if, for example, such an occlusion occurs in a portion of the vasculature that supplies vital organs with blood or other necessary fluids.
To treat these diseases, a number of different therapies have been developed. While a number of effective invasive therapies are available, it is desired to develop non-invasive therapies as well. Non-invasive therapies may be more desirable because of the possibility of decreased chances of infection, reduced post-operative pain, and less post-operative rehabilitation. Drug therapy is one type of non-invasive therapy developed for treating vascular diseases. Clot-dissolving drugs have been employed to help break up blood clots which may be blocking a particular vascular lumen. Other drug therapies are also available. Further, non-invasive intravascular treatments exist that are not only pharmaceutical, but also physically revascularize lumens. Two examples of such intravascular therapies are balloon angioplasty and atherectomy, both of which physically revascularize a portion of a patient's vasculature.
Balloon angioplasty is a procedure wherein a balloon catheter is inserted intravascularly into a patient through a relatively small puncture, which may be located proximate the groin, and intravascularly navigated by a treating physician to the occluded vascular site. The balloon catheter includes a balloon or dilating member which is placed adjacent the vascular occlusion and is then inflated. Intravascular inflation of the dilating member by sufficient pressures, on the order of 5 to 12 atmospheres or so, causes the balloon to displace the occluding matter to revascularize the occluded lumen and thereby restore substantially normal blood flow through the revascularized portion of the vasculature. It should be recognized that this procedure does not remove the matter from the patient's vasculature, but displaces and reforms it.
While balloon angioplasty is quite successful in substantially revascularizing many vascular lumens by reforming the occluding material, other occlusions may be difficult to treat with angioplasty. Specifically, some intravascular occlusions may be composed of an irregular, loose or heavily calcified material which may extend relatively far along a vessel or may extend adjacent a side branching vessel, and thus may not be prone or susceptible to angioplastic treatment. Even if angioplasty is successful, there is a chance that the occlusion may recur. Recurrence of an occlusion may require repeated or alternative treatments given at the same intravascular site.
A relatively new technique to reduce the recurrence of occlusion after a balloon angioplasty procedure involves providing a stent at the revascularized site. A stent is typically a hollow tube, typically braided, that can be inserted into the vascular of a patient in a compressed form. Once properly positioned at a desired site, the stent is expanded to hold the vessel open in an attempt to prevent restenosis. While this technique can help maintain blood flow past the site, it has been found that the occluding material often migrates through the interstices of the stent braid, and may again occlude the vessel. This phenomenon is sometimes referred to as interstitial hyperplasia.
Accordingly, attempts have been made to develop other alternative mechanical methods of non-invasive, intravascular treatment in an effort to provide another way of revascularizing an occluded vessel and of restoring blood flow through the relevant vasculature. These alternative treatments may have particular utility with certain vascular occlusions, or may provide added benefits to a patient when combined with balloon angioplasty, drug and/or stent therapies.
One such alternative mechanical treatment method involves removal, not displacement of the material occluding a vascular lumen. Such treatment devices, sometimes referred to as atherectomy devices, use a variety of material removal means, such as rotating cutters or ablaters for example, to remove the occluding material. (The term "atherectomy device" as used throughout the specification refers to ablation devices for use in any portion of a patient's vasculature. Thus, while the atherectomy devices provided in accordance with preferred embodiments of the present invention are well suited for use in the coronary arteries, their use is not limited to the coronary arteries.) The material removal device is typically rotated via a drive shaft that extends out of the vascular of the patient and to an electric motor.
In operation, an atherectomy device is typically advanced over a guide wire placed in vivo until the material removal device is positioned just proximal to the occluded site. The motor is used to rotate the drive shaft and the material removal device, and the material removal device is moved through the occluded vessel. The material removal device removes the material from the vessel, rather than merely displacing or reforming the material as in a balloon angioplasty procedure.
A potentially negative characteristic for all atherectomy devices is the unwanted perforation of a vessel wall by the material removal device. This can occur when the material removal device improperly engages the vessel wall, for example when the material removal device is not oriented substantially parallel to the axis of the vessel. In this situation, the material removal device (e.g., cutter or abrasive ablater) may improperly engage the vessel wall and cause unwanted damage thereto.
Similarly, an atherectomy device may cause damage to an in vivo stent when used to remove occluding material from within the stent caused by, for example, interstitial hyperplasia. Even a properly oriented material removal device may damage a stent. If the cutter or ablater of a typical atherectomy device engages a stent, particulates of the stent and/or material removal device may be removed and introduced into the vasculature of the patient, which can cause complications. To reduce this risk, the material removal device typically has an outer diameter that is substantially less than the inner diameter of the stent. It is believed that this may reduce the risk that the material removal device will engage and thus damage, the stent. A limitation of this approach is that a substantial gap typically must be provided between the material removal device and the stent. This may reduce the amount of occluding material that can be removed from within the stent. Accordingly, the stent will likely become occluded again sooner than if the outer diameter of the material removal device could more closely match the inner diameter of the stent, and remove more of the occluding material.
Given the above-discussed considerations, it would be desirable to provide an atherectomy device that can reduce the risk of damage to a vessel wall and/or an in vivo stent. In particular, it would be advantageous to provide an atherectomy device that can align the burr cutting action with a path through the stenosed vessel while removing unwanted material and yet not cause excessive wear on the vessel walls. The present invention fulfills these needs, and provides further related advantages.